The present invention relates to a storage battery arrangement which can be better monitored, in particular a storage battery arrangement for an electrically driven vehicle.
Storage battery arrangements having a plurality of cells connected in series and/or in parallel are used in electrically driven vehicles, for example a purely electrical drive or a so-called hybrid drive which comprises both an internal combustion engine and an electric motor. The cells may be combined to form modules. It is also possible to use two storage battery arrangements each having a plurality of cells connected in series. The storage battery cells may be so-called lithium ion batteries. During operation, that is to say during charging or discharging, the state of the storage battery cells must be monitored. For example, the state of charge of the cells must be permanently monitored. For this purpose, a separate electronic monitoring device is provided for each cell. Each electronic monitoring device is connected to a central battery monitoring device, for example by means of a CAN bus. A technical challenge in this case is the high voltage difference of several 100 V from the first storage battery cell to the last storage battery cell. Consequently, complicated insulation must be provided on the CAN bus and on the central battery monitoring device.
DE 11 2012 002 265 T5 discloses an impedance analysis in connection with a solid-state secondary battery.
WO 2009/024355 A1 discloses a method for determining impedance spectra for a location-selective representation of the capacitance distribution, resistance distribution and energy density distribution in a storage battery.
An object of the invention is providing an improved storage battery arrangement and an improved method for determining the state of a storage battery cell which does not require any complicated insulation.
A storage battery arrangement according to the invention comprises a plurality of storage battery cells connected in series and/or in parallel, a central network node, a plurality of cell network nodes and a control device. The central network node is designed to transmit data by means of the storage battery cells. The central network node is connected to the series circuit of storage battery cells, for example in a manner free of a reference potential by means of at least one coupling capacitor. Each of the plurality of cell network nodes is designed to transmit data by means of the storage battery cells. Each cell network node is connected in parallel with a storage battery cell. The control device is designed to instruct at least one cell network node to apply a test signal at at least one predetermined frequency to a first storage battery cell to which the first cell network node is connected, and to instruct a second cell network node which is connected to a second storage battery cell to determine at least one state of the second storage battery cell on the basis of the signal response of the second storage battery cell to the test signal.
The central network node and the plurality of cell network nodes form a network which transmits data by means of an energy supply line and a plurality of storage battery cells. Such data transmission via the power supply system is referred to as Power Line Communication (PLC) in energy engineering.
The test signal may have a predetermined frequency. This makes it possible to determine the resistances and capacitances in the storage battery cell. For example, a storage battery cell expands during charging, as a result of which the frequency response changes. The predetermined frequency may be in a range of approximately 1 MHz to approximately 30 MHz.
The invention has the advantage that it is possible to dispense with an additional bus and insulation of the bus as a result of the fact that data are transmitted by means of the storage battery cells and the lines connecting the storage battery cells. This makes it possible to reduce the effort needed to produce the storage battery arrangement and to maintain it.
The test signal may be a signal from an impedance analysis and/or a signal from a frequency response analysis. The impedance analysis and/or the frequency response analysis may use the carrier frequencies of a transmission method which uses a plurality of different carrier frequencies. The transmission method may be an OFDM (Orthogonal Frequency Divisional Modulation) method.
The cell network node may use, as the test signal, a signal which is used to determine the bandwidth of a transmission channel in the case of a plurality of potential carrier frequencies. This has the advantage that means and algorithms which are already present can be concomitantly used to determine the state of a storage battery cell even though these means were originally provided for the purpose of checking the bandwidth of a transmission channel. Such a method is referred to as “channel sounding” in the field of PLC.
The cell network node and/or the control device may be designed to determine at least the state of charge of the storage battery cell, the aging of the storage battery cell, the internal resistance of the storage battery cell, the temperature of the storage battery cell, and/or the mechanical stress acting on the storage battery cell by means of the test signal. The state of charge, the aging, the internal resistance, the temperature and the mechanical stress acting on the storage battery cell change the frequency response. These states can therefore be determined by means of a test signal which preferably has a plurality of predetermined frequencies. The cell network node may be designed to check the attenuation of the test signal and the signal-to-noise ratio at predetermined frequencies if the test signal is applied to the storage battery cell.
The invention also relates to a motor vehicle having the storage battery arrangement described above.
The invention also relates to a method for determining the state of a storage battery cell of a storage battery arrangement having a series circuit and/or a parallel circuit of a plurality of storage battery cells, a cell network node being connected in parallel with each of the storage battery cells. The method transmits an instruction signal by means of at least one first storage battery cell, with which a first network node is connected in parallel, from a central network node to a second network node which is connected in parallel with a second storage battery cell. A test signal at at least one predetermined frequency is applied to the first storage battery cell by means of the first cell network node if the instruction signal is received. A state of the second storage battery cell is determined on the basis of the signal response of the second storage battery cell to the test signal if the instruction signal is received.
The method can be developed in the manner described above with respect to the storage battery arrangement. The method can also check the states of the storage battery cell which were described above with reference to the storage battery arrangement.
The test signal may be a signal from an impedance analysis, a signal from a frequency response analysis, a signal which corresponds to the carrier frequencies of a transmission method having a plurality of different carrier frequencies, and/or a signal which corresponds to the carrier frequencies of an OFDM method.
The method may determine the attenuation of the test signal at a predetermined frequency. Alternatively or additionally, the method may determine the signal-to-noise ratio at a predetermined frequency.
The invention also discloses a computer program product which carries out the method described above when it is loaded into the memory of a computer having a processor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.